1. Field of the Invention
The present invention relates to an apparatus and a method for controlling operation of a reciprocating compressor operating a compressor by being inputted a certain stroke command value, and in particular to an apparatus and a method for controlling operation of a reciprocating compressor which is capable of operating a reciprocating compressor stably by detecting a phase difference of a current and a voltage and a phase difference of a current and a velocity and using an inflection point of the phase difference.
2. Description of the Prior Art
Generally, a compressor is for pressurizing refrigerant vapor (compressing refrigerant vapor) in order to make condensing of refrigerant vapor evaporated in a vaporizer easier. By the operation of the compressor, heat can be transmitted from a cold side to a warm side by a refrigerant circulating inside a refrigerating apparatus while repeating a condensing and a vaporizing processes.
These days various types of compressors are used, among them a reciprocating compressor is generally used. The reciprocating compressor pressurizes vapor by a piston moving up and down inside a cylinder, particularly when the reciprocating compressor is used for a refrigerator or an air conditioner, a pressure ratio can be varied by varying a stroke voltage applied to the reciprocating compressor, accordingly it is advantageous to a variable refrigerating capacity control.
FIG. 1 is a block diagram illustrating a construction of an apparatus for controlling operation of a reciprocating compressor in accordance with the prior art. As depicted in FIG. 1, an apparatus for controlling operation of a reciprocating compressor includes a voltage/current detecting unit 13 detecting a voltage and a current generated in a reciprocating compressor, a stroke calculating unit 11 calculating a stroke (a distance between a top dead center and a bottom dead center of a piston) by using the voltage and the current detected in the voltage/current detecting unit 13 and outputting it, a comparator 10 comparing the calculated stroke with a certain stroke command value inputted by a user and outputting a comparison signal according to the comparison result, a stroke controller 12 increasing or decreasing a stroke voltage according to the comparison signal from the comparator 10 and outputting it, a microcomputer 14 outputting a switching control signal according to the stroke voltage outputted from the stroke controller 12, and an electric circuit unit 15 applying a certain voltage to the reciprocating compressor according to a switching control signal of the microcomputer 14.
The control operation of the reciprocating compressor in accordance with the prior art will be described.
In the reciprocating compressor, when a stroke voltage is outputted by being inputted a certain stroke command value from a user, a stroke (a distance between a top dead center and a bottom dead center of the piston) is varied by an up and down motion of a piston of a cylinder, a refrigerating gas inside the cylinder is transmitted to a condenser through a discharge valve, accordingly a refrigerating capacity can be adjusted.
Herein, as depicted in FIG. 2, according to the increase of the stroke by the stroke voltage, when the voltage and the current generated in the reciprocating compressor are detected and applied to the stroke calculating unit 11 as shown at step ST10, the stroke calculating unit 11 calculates a stroke by using the voltage and the current detected from the voltage/current detecting unit 13 as shown at step ST11. Accordingly, the comparator 10 is inputted, compares the stroke command value with the stroke calculated in the stroke calculating unit 11 and applies a comparison value to the stroke controller 12 as shown at step ST12, and the stroke controller 12 varies the stroke voltage according to the comparison value and applies it to the microcomputer 14 as shown at step ST13. After, the microcomputer 14 outputs a switching control signal by the voltage applied from the stroke controller as shown at step ST14 and operates the reciprocating compressor as shown at step ST15.
Herein, when the stroke value calculated in the stroke calculating unit 11 is smaller than the stroke command value, the stroke controller 12 increases a stroke voltage, when the stroke value calculated in the stroke calculating unit 11 is larger than the stroke command value, the stroke controller 12 decreases a stroke voltage and applies it to the microcomputer 14.
Herein, the stroke calculating unit 11 is inputted a motor constant xcex1 (constant for converting an electric power into a mechanical power), Rac (a loss value due to resistance such as a copper loss or an iron loss), a voltage VM between both ends of a motor, etc. and calculates a velocity of a piston and a stroke by below equations.
xe2x80x83Velocity=VMxe2x88x92Racixe2x88x92L di/di
Stroke=1/xcex1∫(Velocity)dt
In the meantime, a stroke of a triac of the electric circuit unit 15 is increased by lengthening a turn on cycle according to a switching control signal of the microcomputer 14, herein the voltage and the current generated in the reciprocating compressor are separately detected in the voltage/current detecting unit 13 and are applied to the stroke calculating unit 11.
Then, the stroke calculating unit 11 calculates a stroke by using the voltage and the current detected from the voltage/current detecting unit 13, the calculated stroke is compared with the stroke command value in the comparator 10 the comparison result is outputted to the stroke controller 12, the stroke controller 12 increases or decreases the stroke voltage, the microcomputer 14 is inputted the stroke voltage outputted from the stroke controller 12 and outputs a switching control signal for controlling a reciprocating compressor to the reciprocating compressor.
In more detail, when the calculated stroke is smaller than the stroke command value, the microcomputer 14 increases a stroke voltage applied to the reciprocating compressor by outputting a switching control signal for lengthening an turn on cycle of the triac, when the calculated stroke is larger than the stroke command value, the microcomputer 14 decreases a stroke voltage applied to the reciprocating compressor by outputting a switching control signal for shortening a turn on cycle of the triac.
In the meantime, the microcomputer 14 detects a load (the outdoor temperature or a condenser temperature, etc.) by installing a sensor at the circumstances of a compressor or a circuit unit of a refrigerator and uses it as basic information for precision control of a refrigerator. For example, the microcomputer 14 detects the temperature through a sensor installed at the surface of the condenser and detects a load.
However, the apparatus and the method for controlling operation of the reciprocating compressor in accordance with the prior art has a serious nonlinearity in the mechanical motion characteristic aspect due to difficulties in measuring accurate current and voltage caused by loss such as a motor constant or a copper loss or an iron loss, it is impossible to perform a precise control with the control method not considering the nonlinearity, in load detecting for precise control of the compressor, the outdoor temperature or a temperature of a condenser is measured through a sensor installed on the surface, after examining each load condition different control algorithm has to be applied according to each condition, accordingly a time delay occurs and the load can not be accurately detected due to the time delay.
In addition, because a reciprocating compressor is controlled with a fixed stroke, a TDC (Top Dead Center) is varied according to increase or decrease of load of a refrigerator. And, because the reciprocating compressor is operated by a quantitative control (control using a constant value required for converting an electric power into a mechanical power, a loss value due to resistance such as a copper loss or an iron loss, an inductance, a current, a voltage between both ends of a motor, etc.), a refrigerating capacity is varied according to characteristics of a motor constant and an apparatus, lots of error elements occur in stroke calculation, accordingly an operation efficiency of the reciprocating compressor is low.
Accordingly, it is an object of the present invention to provide an apparatus and a method for controlling operation of a reciprocating compressor which is capable of performing a TDC (Top Dead Center) control of a piston by using an inflection point about phase difference of an input voltage and a current.
It is another object of the present invention to provide a method for controlling operation of a reciprocating compressor which is capable of performing a precise control by determining an operation mode by detecting a load with a reference value of a phase difference of a voltage and a current.
It is still another object of the present invention to provide a method for detecting a phase of a reciprocating compressor which is capable of detecting precisely a phase difference of two signals and reducing a cost by detecting a phase of a signal by a digital mode.
In order to achieve the above-mentioned objects of the present invention, an apparatus for controlling operation of a reciprocating compressor in accordance with the present invention includes an electric circuit unit operating a reciprocating compressor by varying a stroke by motion of a piston, a phase difference detecting unit detecting a phase difference about a current and a voltage from the electric circuit unit, a phase inflection point detecting unit detecting a phase inflection point by being inputted the phase difference, and a stroke controlling unit being inputted the phase inflection point detected from the phase inflection point detecting unit and applying a stroke voltage corresponded to the phase inflection point to the electric circuit unit.
In order to achieve the above-mentioned objects, a method for controlling operation of a reciprocating compressor in accordance with the present invention includes a first process for operating a reciprocating compressor for a certain time with a fixed stroke and detecting a phase difference of a voltage and a current at the operation, a second process for judging whether a reference value of a phase difference in the first process is larger or smaller than a certain value (xcex1xcex2: xcex1 less than xcex2), a third process for performing avoidance operation of the reciprocating compressor according to a stroke tremble while operating the reciprocating compressor with a fixed stroke when the reference value of the phase difference is smaller than the certain value (xcex1) in the judging result, a fourth process for performing avoidance operation of the reciprocating compressor according to a stroke tremble while operating the reciprocating compressor with a fixed stroke when the reference value of the phase difference is larger than the certain value (xcex2) in the judging result, and a fifth process for performing avoidance operation of the reciprocating compressor according to a stroke tremble and a size of a refrigerating capacity while operating the reciprocating compressor with a stroke having a phase inflection point when the reference value of the phase difference is between certain values (xcex1, xcex2: xcex1 less than xcex2) in the judging result,
In order to achieve the above-mentioned objects, a method for detecting a phase of a reciprocating compressor includes a first process for detecting first and second zero voltages by sampling a first and a second analog signals with a certain sampling cycle, a second process for generating a first and a second phase signals using the first and the second zero voltages detected in the first process, and a third process for detecting a phase difference signal by performing a logical operation of the first and the second phase signals generated in the second process.